Consumer voice over internet protocol (VoIP) services offered by many communications service providers, for example, internet telephony service providers (ITSPs) are established by installing an analog telephone adapter at a subscriber's premises. The analog telephone adapter bridges an analog telephone, for example, a plain old telephone system (POTS) phone to the internet by exchanging signaling messages and media data such as audio data with the communications service providers. To use the VoIP service, the subscriber has to just pick up the POTS phone to make and receive calls in a manner similar to a conventional home phone service.
A session initiation protocol (SIP) is a typical VoIP signaling protocol with a message format similar to the hypertext transfer protocol (HTTP). While the SIP may be transported securely over a transport layer security (TLS) protocol and/or a secure sockets layer (SSL) protocol, most communications service providers transport the SIP over a user datagram protocol (UDP) or a transmission control protocol (TCP). In the SIP, the transport addresses for communication between peers or users are embedded in signaling messages. A transport address is an internet protocol (IP) address: port combination where packets or messages are sent from or received at a peer. The transport address is of two types, for example, a public transport address and a private transport address. Users anywhere in the world can send packets to a public transport address. Only users in the same private network can send packets to a private transport address. Each user is required to indicate his/her transport address to another user for sending signaling messages and media data to each other.
An analog telephone adapter typically connects to a network via a home router. The analog telephone adapter indicates private transport addresses in session initiation protocol (SIP) messages. The home router replaces the private transport addresses in the IP header of the packets carrying these SIP messages with corresponding public transport addresses through network address translation (NAT), before the SIP messages are forwarded. Many home routers also have a gateway which is a network node equipped for interfacing a communications network with another communications network that uses different protocols. The gateway, for example, a SIP application layer gateway (ALG) is configured to augment VoIP signaling or SIP through the NAT. The SIP ALG replaces the private transport addresses in the SIP messages with corresponding public transport addresses before forwarding the SIP messages. The modified SIP messages appear to be corrupted if the SIP ALG is incorrectly configured and are therefore dropped by the communications service provider. Moreover, the communications service provider may be misled into believing that the analog telephone adapter is connected directly to the internet without a NAT and handles the SIP message differently, causing a communication breakdown between the analog telephone adapter and the communications service provider.
With conventional analog telephone adapter devices, communications service providers spend a lot of time diagnosing session initiation protocol (SIP) application layer gateway (ALG) related issues reported by their subscribers. To resolve this, the subscribers are advised to disable the SIP ALG option in the home router settings, or to replace the home router with a router that does not have the SIP ALG feature, or to disable the SIP ALG feature by reconfiguring the home router. However, reconfiguration is an expensive option for the communications service provider to support subscribers. Sometimes, frustrated subscribers may decide to drop the service of the communications service provider altogether. Hence, there is a need for an analog telephone adapter that can detect whether an ALG, for example, the SIP ALG exists in the path between the analog telephone adapter and the communications service provider, or assist the communications service provider to detect the presence of the SIP ALG, and that can bypass the SIP ALG.
The presence of the session initiation protocol (SIP) application layer gateway (ALG) in home routers creates a major support issue for communications service providers, and many diagnostic steps are required before a trouble-ticket can be diagnosed as a SIP ALG problem. Conventional analog telephone adapter devices can neither detect the presence of the SIP ALG nor bypass the ALG in a network path between the analog telephone adapter and the communications service provider. These conventional analog telephone adapter devices cannot explicitly inform the communications service provider whether the SIP ALG exists in the network path between the analog telephone adapter and the communications service provider. These analog telephone adapters also do not offer a feasible way to bypass the SIP ALG if the SIP ALG is indeed present in the network path. To apply itself, the ALG must first recognize that the received media message is an SIP message. Although a few conventional analog telephone adapter devices may in effect bypass the ALG by transporting the SIP over a secure channel, such a solution is impractical to most commercial communications service providers as this solution requires a major equipment upgrade. Hence, there is a need for a method and a system that detects the presence of the SIP ALG and bypasses the ALG without requiring the communications service providers to upgrade their equipment, or without replacing and/or reconfiguring subscribers' home routers.
Hence, there is a long felt but unresolved need for a method and a system that detects the presence of an application layer gateway (ALG), for example, a SIP ALG in a network path between the analog telephone adapter and the communications service provider. Moreover, there is a need for a method and a communications management system that transmits a media message by bypassing the ALG in the network path between the analog telephone adapter and the communications service provider.